1. Field of the Invention
The present invention relates to a small-sized commutator motor and in particular to a carbon brush holder for an electric power tool wherein a carbon brush is replaceably installed and no conductive insert is present at the peripheral portion of a slot for receiving the carbon brush, so that assembling of the carbon brush holder and the carbon brush is facilitated and heat produced from the carbon brush is easily dissipated, thereby enhancing the function of the carbon brush.
2. Description of the Prior Art
In general, a small-sized commutator motor comprises a rotary part having an armature and a commutator, and a stationary part having a field coil, a field iron core and a brush, wherein both of the rotary part and the stationary are mounted within a motor housing and, wherein the brush is formed from a carbon material having good commutating characteristics and excellent durability.
The carbon brush conducts electric current while being in contact with the surface of the commutator revolving at a high velocity, and thus the surface wears out and heat is produced due to the frictional contact with the revolving commutator and sparks generated by electric current. In this connection, a spring is used as elastic forcing means to compensate for the wear of the contacting surface of the carbon brush.
As shown in FIG. 1, a carbon brush holder well-known in the art comprises an insert A formed from brass. The insert is molded by a plastic material B or assembled by inserting a cartridge-formed brass insert to a ready-molded plastic housing. However, this carbon brush holder has a disadvantage that since the insert serves as an electric conductor and the carbon brush inevitably undergoes frictional contact with the insert A, excessive heat is generated by electric short phenomena and thus the life span of the carbon brush is substantially reduced.
Taking the above problem into consideration, a new construction as shown in FIG. 2 was developed, wherein the new construction comprises a through-hole D formed within the holder body to receive a lead terminal, the through-hole being extended between the top and bottom portions of the holder body, and a conductive wire E extended from a stator being connected to the lead terminal G using a screw F, thereby eliminating a nonferrous conductive insert as shown as "A" in FIG. 2. By such a new construction, it has become possible to prevent the short phenomena generated by electric current flowing on the side surfaces of the carbon brush, and productivity has been somewhat improved. However, the new construction has several problems in that the lead terminal receiving through-hole is difficult to form, it is difficult to smoothly connect the wire to the terminal when the through-hole is formed in a deformed shape, and it is inconvenient to assemble since the wire is connected by the screw.